Pesticides used in the home may be slightly increasing the risk of children developing cancers such as leukemia or lymphoma, a review of published studies suggests.

An analysis of 16 studies dating back to the 1990s found that children who were exposed to indoor home pesticides had a slightly increased risk of developing the blood cancer, researchers report.

The studies all compared children with cancer to healthy children while collecting data on past pesticide exposure using parent interviews.

Although the studies suggest a link, that is not the same as proving a cause-and-effect relationship of pesticides and cancer, the researchers acknowledge in their study appearing in the journal Pediatrics.

Even if such a relationship is assumed, it would raise a number of questions, they point out.

"We don't know 'how much' exposure it takes, or if there's a critical window in development," says senior researcher Chensheng (Alex) Lu of the Harvard School of Public Health in Boston.

"Is the window during pregnancy? Or even before pregnancy?" says Lu, professor of environmental exposure biology. "That will take a much deeper investigation."

Their analysis showed a statistically significant association between home pesticide exposure during childhood and "childhood hematopoietic malignancies" (blood cancers), the researchers wrote.

Although such cancers are rare — leukemia, for example, affects just five in 100,000 U.S. children — they are common types of childhood cancers.

"Childhood cancers are increasing year by year in this country, (and) there is disagreement about what is contributing to that, but pesticides have always been on the radar," says Lu.

Indoor pesticides are a particular problem because, unlike pesticides used outdoors around the house, there is less fresh air circulating indoors that can dilute the pesticide chemicals, Lu notes.

Those chemicals can remain on surfaces on which children eat or play, he says, and children age 12 or younger seem to be the most vulnerable to possible cancer-causing impacts of pesticides.

The ingredients in pesticides designed to kill insects may be causing genetic mutations in blood cells, leading to leukemia or lymphoma, Lu suggests.

Other experts said the study findings were important and should be studied closely.

"We are starting to get to the place where there is enough science, it just starts to add up to say that we can't really ignore anymore ... the role of environmental factors like pesticides in health," says Dr. Catherine J. Karr, director of the University of Washington's Pediatric Environmental Health Specialty Unit.